1. Field of the Invention
The present invention relates to a wrapping film suitably used as a wrapping film for packaging use, particularly for household use. More specifically, it relates to an adhesive wrapping film satisfactory in its adhesive sealing property and drawing-out property and superior in its visual recognizability of contents.
2. Description of the Related Art
A wrapping film for household use is employed for over-wrapping foods put on a vessel for the purpose of mainly storing foods in a refrigerator or a freezer or heating foods in a microwave. For this reason, for example, it is required that the wrapping film has transparency and a moderate modulus of elasticity, the film is stable so as to be free from perforation, welding to a vessel or self-deformation even when subjected to heating in a microwave oven or the like, and further the film exhibits a moderate self-adhesive sealing property or adhesive sealing property against a vessel within a range of from a low temperature to a high temperature.
As a commercially available wrapping film for household use, there are a film composed mainly of polyvinylidene chloride based resin, which is most easily and extensively used, a film composed mainly of polyethylene based resin, which is extensively used in spite of remarkable inferiority in its wrapping qualification, and others composed mainly of plasticized polyvinyl chloride based resin, poly 4-methylpentene-1 based resin or the like.
Generally speaking, the wrapping film is rolled round a paper tube, and in such a state (which is called a rolled wrapping film) received in a decorated box to be used in a manner such that dinner vessels or the like are covered therewith by hand to perform a package. For this reason, the wrapping film is required to have a high adhesive sealing property, so that a content in a vessel, even if liquid, is not spilt in sending in or out of a refrigerator or the like, as well as a visual recognizability of wrapped goods (transparency of the wrapping film). Whereas, there has been left a problem in that when a self-adhesive sealing property of the rolled wrapping film is high, the film becomes difficult to be peeled from each other and results in cutting, when drawn out from the decorated box.
A wrapping film obtained in consideration of the problem is disclosed in JP-A 11-501895. Herein, there is proposed a wrapping film having a concavo-convex form on a surface of a substrate layer, wherein a size of the concavo-convex is larger than a thickness of said layer, and only the concave portion is partially filled with a tackifier. The wrapping film is described to satisfy both the adhesive sealing property and the drawing-out property at the same time. However, the wrapping film is found to exhibit a 180xc2x0 peeling strength of not less than 1 oz/inch (=about 11 g/cm width) when applied with a compressive strength of not less than 0.1 psi (=about 7 g/cm2), which is said to be xe2x80x9coperation by usersxe2x80x9d, and therefore, there is left a problem in that when a long length film is rolled round, it may happen that a rolling pressure of the film exceeds the compressive strength applied by users, and as a result, it is difficult to satisfy both the adhesive sealing property and the drawing-out property at a practical level.
In addition, from the fact that a size of the concavo-convex formed on the surface of the substrate layer is larger than the thickness of the substrate layer, and moreover the tackifier is discontinuously applied on said substrate layer (no tackifier is present on the convex portion of the concavo-convex of the substrate layer), there is also left a problem in that a space is easily produced as far as the compressive strength by users is not applied to both the film and materials to be bonded under a perfect condition, and as a result, the content, particularly if liquid, is easily spilt. Further, the scattering of light promotes loss of transparency, and therefore transparency of the wrapping film becomes insufficient to create a severe problem on the visual recognizability of the wrapped goods.
An object of the present invention is to provide a wrapping film, which is superior in its drawing-out property without detriment to its high adhesive sealing property, and which is satisfactory in its visual recognizability of wrapped goods.
The present inventors have undertaken extensive studies from three viewpoints of the adhesive sealing property, the drawing-out property and the transparency, and as a result, it has been found that a film having a fixed relation among a concavo-convex size of a substrate layer, a concavo-convex size of a tackifier layer and a thickness of a tackifier layer can exhibit the most suitable wrapping qualification. Thereby, the present invention has been obtained.
The present invention is as follows:
An adhesive wrapping film having a continuous tackifier layer (A) on at least one side surface of a substrate layer (B) whose surface has a concavo-convex form, wherein a thickness of the tackifier layer at the concave portion of the substrate layer is larger than that at the convex portion of the substrate layer, and a thickness of the substrate layer BAV, a thickness of the tackifier layer at the concave portion of the substrate layer Amax, a ten-point average roughness of the surface of the tackifier layer corresponding to a height of the convex portion of the tackifier layer RZ(A), and a ten-point average roughness of the surface of the substrate layer corresponding to a height of the convex portion of the substrate layer RZ(B) satisfy a relation of the following conditional expressions (1) and (2):
(1) Amax less than RZ(B) less than BAV 
(2) RZ(A) less than RZ(B).
That is, the present invention comprises a combination of the following three conditions.
1) The film in accordance with the present invention is provided with a concavo-convex on one or both side surfaces of a substrate layer (B) and a continuous tackifier layer (A) formed on said substrate layer to form a lamination structure, wherein a ten-point average roughness of the concavo-convex (RZ(B)) is smaller than a thickness of said substrate layer (BAV).
2) On the concavo-convex surface of said substrate layer is provided a tackifier layer having a thickness (Amax) and a ten-point average roughness (RZ(A)), which are smaller than the ten-point average roughness of the concavo-convex of said substrate layer (RZ(B)).
3) A thickness of the tackifier layer at a concave portion of said substrate layer is larger than that of the tackifier layer at a convex portion thereof. That is, the thickness of the tackifier layer is formed so as to be thickest at a valley portion of the concavo-convex and minimum at a summit portion thereof, provided that the tackifier layer is a continuous layer.
The most different point between the present invention and the prior art is that a specific concavo-convex structure is provided on the surface of a substrate layer, a tackifier layer having a thickness smaller than a height of the concavo-convex is provided on both the concave and convex portions of the surface of the substrate layer, and moreover a thickness of the tackifier layer at the concave portion is smaller than that of the tackifier layer on the convex portion, whereby the structure is made so as to have a high tackifying concave portion and a low tackifying convex potion which are present as a mixture.
The film having the above-mentioned structure can exhibit a satisfactory visual recognizability of wrapped goods. In other words, it is possible to make a clouding degree (Haze), which is an index of transparency of a film, from more than 0% to less than 50%. Further, the film can exhibit a drawing-out property free from blocking when a rolled film is drawn out, that is, the film can exhibit a drawing-out force of not more than 80 g/300 mm width without detriment to a high adhesive sealing property, whereby both properties conflict with each other can be satisfied.